For many people, the answer is "as long as possible." Some people are deathly afraid of getting older - maybe they've seen their parents or grandparents descend into dementia or become blind, deaf and crippled.
If you've been following this blog, you already know that old age doesn't necessarily mean being fragile and useless. Chinese history is full of stories about qi gong masters who live full, vital lives, with the same bodily functions at age 80 as they had at age 40. Heck, forget history, just go to Chinatown. New York's Chinatown is full of old Chinese people exercising, walking, shopping, and elbowing their way down the crowded streets in search of the best bargain. You can see the same thing in Southern California, but to a lesser degree because everyone here is in a car.
There are also people who are indifferent about living a long time, as long as they accomplish their goals. These people often have exciting lives, full of sex, drugs, adventure, and high stress situations. The payoff is they can often pack incredible achievements into their short lives, making millions or billions of dollars, or lighting the world on fire with some kind of outstanding art or music.
Which way is better? Given the bend of this blog, you might expect an endorsement of the quiet, simple life, full of meditation and bland food. The fact is, how you live your life is up to you, and no one can live it for you. As long as you're fulfilling your responsibilities, no one can shake their finger at you.
It's my personal belief that everyone has special talents and abilities, and it is your responsibility to develop them fully, so that others may benefit. Don't waste your life! Don't waste it on excessive drinking, but don't waste it on a purposeless office job either. Don't waste your life on partying, but don't waste it watching television either. Once you discover your purpose in life, everything else can become subordinate to that, including your health. Just keep in mind that for most people, taking the time to maintain optimal health will give you the tools to fulfill your purpose with more skill, energy and passion than if you're running on empty.